Currently, specialty polyolefins, such as ethylene-methyl methacrylate (EMA), ethylene-ethyl acrylate (EEA), ethylene-butyl acrylate (EBA), and ethylene-acrylic acid (EAA) are made by high temperature, high pressure free radical polymerizations. These polymers have been used in medical packaging, disposable gloves, cable compounding, adhesives, and many other applications. However, these materials are expensive.
Since the late 1990s, olefin polymerization catalysts that incorporate late transition metals (especially iron, nickel, or cobalt) and bulky α-diimine ligands (or “bis(imines)”) have been investigated. These late transition metal catalysts are of interest because, unlike the early transition metal metallocenes or Ziegler catalysts, the late transition metal catalysts can tolerate and incorporate polar comonomers into polyolefins. See U.S. Pat. Nos. 5,866,663 and 5,955,555.
Recently, new late transition metal catalysts that contain isoindoline ligands have been developed. See co-pending application Ser. No. 09/947,745, filed on Sep. 6, 2001. These catalysts have showed higher activity than the bis(imines)-based late transition catalysts. Moreover, these catalysts are relatively easy to prepare. However, these catalysts have not been explored for the use in the preparation of olefin-acrylic copolymers.
Compared to the conventional free radical polymerization, late transition metal catalysts have great ability in tailoring of critical polymer properties: molecular weight, crystallinity or melting point, and polydispersity. Therefore, the late transition metal catalysts may provide better product quality and production consistency. Also, the late transition metal catalysts do not require high temperature and high pressure polymerization. They avoid the use of explosive peroxides. Thus, the late transition metal catalyst polymerization may provide a safer and more cost-effective alternative to the existing free radical technology.
In summary, exploring new methods for the preparation of olefin-acrylic copolymers is important to the industry. More particularly, the methods would use the newly developed late transition metal catalysts. Ideally, the catalysts would not only be able to tolerate the acrylic comonomers but also have high activity and be easy to make.